Embodiments disclosed herein generally relate to blowout preventers used in the oil and gas industry during oil and gas well drilling and work over to prevent escape of well bore pressure into the outside environment in the event of an unexpected pressure “kick” due to the influx of formation fluid or other uncontrolled situations. Specifically, embodiments discussed herein relate to an annular-spherical blowout preventer design having multiple pistons and glands.
Well control is an important aspect of oil and gas exploration. For example, when drilling a well, safety devices must be put in place to prevent damage to equipment and, most importantly, to personnel resulting from unexpected events associated with drilling operations. Because of safety conditions and risk of blowouts devices known as blowout preventers (BOPS) are installed above the wellhead at the surface or on the sea floor in deep water situations to effectively seal a wellbore until measures can be taken to control the kick. Blowout preventers are large, specialized high-pressure valves or similar mechanical devices, typically installed redundantly in stacks and used to seal and control downhole pressure and monitor oil and gas wells to ultimately prevent the uncontrolled flow of liquids and gases during well drilling operations. Blowout preventers come in a variety of styles, sizes and pressure ratings and often several individual units serving various functions are combined to compose a blowout preventer stack. Some of the functions of a blowout preventer system include, but are not limited to, confining well fluid to the wellbore, providing a means to add fluid to the wellbore, allowing controlled volumes of fluid to be withdrawn from the wellbore, regulating and monitoring wellbore pressure, and sealing the wellhead.
In addition to controlling the downhole pressure and the flow of oil and gas, blowout preventers are intended to prevent tubing, tools and drilling fluid from being blown out of the wellbore when a blowout threatens. Blowout preventers are critical to the safety of crew, rig and environment, and to the monitoring and maintenance of well integrity. Thus, blowout preventers are intended to be fail-safe devices. Multiple blowout preventers of the same type are frequently provided for redundancy, an important factor in the effectiveness of fail-safe devices.
There are two major types of blowout preventers, annular and RAM. Annular BOPs are usually mounted to the very top of a BOP stack. The drilling crew then typically mounts a predetermined number of RAM BOPs below the annular blowout preventer. Blowout preventers were developed to cope with extreme erratic pressures and uncontrolled flow, often referred to as formation kick, emanating from a well reservoir during drilling. Kicks can lead to a potentially catastrophic event known as a “blowout.” If a kick is detected, the annular is usually closed first and then the RAM is used as a backup if the annular should fail. Often times during operation BOPs are damaged and repair is difficult if not impossible when dealing with internal component damage such as pistons.
In drilling a typical high-pressure well, drill strings are routed through a blowout preventer stack toward the reservoir of oil and gas. As the well is drilled, drilling fluid, “mud”, is fed through the drill string down to the drill bit, “blade,” and returns up the wellbore in the ring-shaped void, annulus, between the outside of the drill pipe and the casing (piping that lines the wellbore). The column of drilling mud exerts downward hydrostatic pressure to counter opposing pressure from the formation being drilled, allowing drilling to proceed. When a kick occurs, rig operators or automatic systems close the blowout preventer units, sealing the annulus to stop the flow of fluids out of the wellbore. Denser mud is then circulated into the wellbore down the drill string, up the annulus and out through the choke line at the base of the BOP stack through chokes until downhole pressure is overcome. If the blowout preventers and mud do not restrict the upward pressures of a kick a blowout results, potentially shooting tubing, oil and gas up the wellbore, damaging the rig, and leaving well integrity in question.